The type of brush rings described above are used to form brushes in different kinds of sweeping trucks and brushing machines. The brush rings being used today usually comprise a ring shaped frame part. In other words, the frame part has been formed to a circumferential shape when viewed from the side. The ring shaped frame part is usually made of thin sheet iron, the thickness of which is, for example, about 1 mm. The bristles have been attached to this kind of frame part, for example, by means of a suitable solidifying attachment mass. This type of brush ring is usually planar.
This type of brush ring, that is partly made of metal, tends to break particularly because of cold, which causes stiffening of the brushes. On such an occasion, the frame sheet iron supporting the brush part of the brush ring opens in certain places, in which case bigger or smaller units of brush parts are released from the brush ring. In addition to the foregoing problem, it is practically impossible to re-use brush rings with metal frames and plastic brushes, because removing the frame sheet iron from the brushes is not economically justified in practice. That is why this type of brush ring is removed as a whole to the dumping area. That is naturally a significant waste problem. Furthermore, when the type of brush rings described above are being used, very strongly built supporting structures must be used, also, such as space rings made of metal, fastening rings etc., which is why a brush formed of this kind of brush rings becomes disproportionately expensive.
On the other hand from Finnish Patent No. 87977, a brush element is previously known, that is entirely made of plastic based material. When applying the method according to the afore-mentioned patent, plastic paste existing essentially in a solid shape is fed onto the melted edge existing at the top edge of the brush preform, that moves along in an essentially upright position, to work the brush ring to its final shape by means of a press mold assembly by forming the frame part and preferably the holding means from the plastic paste. However, arrangements explained in Finnish Patent No. 87977 in particular for feeding the plastic paste on top of the melted edge of the brush preform are insufficient when being carried out in practice. This leads to the plastic paste becoming unevenly distributed on the brush preform. This leads furthermore to the result that, when pressing the brush preform to bring out a final brush ring, the final brush ring is not adequately as homogeneous. This results in many significant disadvantages in practice, when the brush ring is being used in a brushing machine, wherein, for example, vibration is caused due to unbalance. Furthermore, due to the above-noted extra wearing of the brushing machine, discomfort in the use of the machine is caused as well. Furthermore, the brush elements being manufactured by the method described in the patent above are planar. Thus, due to wearing of the brushes, the brushing of the brush formed of the brush rings becomes discontinuous in the longitudinal direction of the brush, particularly in the jointing points of the brush rings. Therefore, the brush is not able to fulfill, to a satisfactory extent, conventional demands that are requested in certain purposes, because material to be brushed may go through the brush without touching the bristles, in which case the brush must be dismantled and the brush rings replaced.